Uptake and metabolism of catecholamines by the human red blood cell

The uptake and metabolism of ¹⁴C-labeled norepinephrine (NE) and epinephrine (E) by the human red blood cell (RBC) was studied in platelet-free blood in vitro. RBC incubated at 37° C. accumulated NE and E against a concentration gradient and reached an equilibrium distribution ratio, intracellular-extracellular concentration, of about 2 at 2 hours. Uptake was temperature dependent and saturable, both phenomena characterizing an active transport system. During the incubation period, increasing concentration of metabolites, identified as the 0-methyl derivative of NE and E, respectively, appeared both in the RBC and in plasma, the concentration of the metabolite in the RBC always exceeding that in the plasma at any given point in time. Treatment with iodoacetate or quinidine resulted in increased ratios of intracellular to extracellular concentration of NE, while ethylenediaminetetraacetate decreased this ratio. Conversely, drugs known to interfere with the uptake and release of catecholamines in the adrenergic neuron and blood platelet were without effect on the ratio of intracellular to extracellular concentration in the red cell.